Investigative and Proof of Concept Testing

The need for thorough investigative testing is well understood and accepted. This is the exploratory phase of testing where the characteristics of the material are established generates the map of general response to various recovery processes. Often this is sufficient if the object is merely to get to know the material, but it is way short if the purpose of the exercise is to arrive at flowsheet for implementation of an actual process.

The next phase involves optimization of the indicated procedures, dotting the i’s and crossing the t’s so to speak. For example, although agitation in cyanide is a good candidate process, what is the effect of cyanide strength, grind, pH? Recovery is normally the criterion by which each of these effects is measured, but even at this stage a good laboratory should be concerning itself with parameters that will have a profound effect upon the practical implantation of the candidate process in a plant. For example, what does the dissolution rate curve look like – is there scope for a drastically reduced residence time, and therefore CIL tank size if the rate curve can be sharpened?

By the end of the optimization phase the behavior of the material is very well understood. A process is probably crystallising well and this too may be sufficient if the objective is a study with some inputs into a financial analysis.

The next logical step which is very often omitted is proof of concept testing. This involves performing the candidate process at sufficient scale to gain confidence in the outcome. The scale must be sufficient to remove any masking effects that may be present in small scale bench tests whilst not being so large as to introduce complications that lose the finesse of the outcome. For example, in a Carbon in leach test that is carried out at larger scale, the amount of carbon generated will be sufficient to enable analysis of base metals adsorbed and even a small scale elution. A larger scale gravity test will enable the actual recovery of a sample of the concentrate which may be required for a downstream process, like smelting. Unless all of these boxes are also ticked, doubts are carried forward into implementation. The Proof of Concept usually involves large batch testing rather than continuous piloting per se. Piloting can be very expensive and has the complication of including mechanical performance fluctuations that can mask the outcome. It has its place, but normally would form yet another phase if POC does not generate the sufficient confidence required – an unlikely occurrence.

PS&A is particularly geared towards this approach. Being primarily minerals processing engineers, practicality is never far from the focus of the objectives and the directing team are well experienced upon actual plants, even some of the very largest. Our laboratory is equipped with POC scale versions of bench lab equipment, for example 7.5” Batch Knelson for large Knelson POC tests vs. the 3” Knelson for investigative work. 1kg bench top agitation vs. 50kg actual TriTank agitation for POC.